# std::regex_match

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< cpp‎ | regex

Defined in header `<regex>` |  |
template< class BidirIt, class Alloc, class CharT, class Traits > bool regex_match( BidirIt first, BidirIt last, std::match_results<BidirIt, Alloc>& m, const std::basic_regex<CharT, Traits>& e, std::regex_constants::match_flag_type flags = std::regex_constants::match_default ); | (1) | (since C++11)
template< class BidirIt, class CharT, class Traits > bool regex_match( BidirIt first, BidirIt last, const std::basic_regex<CharT, Traits>& e, std::regex_constants::match_flag_type flags = std::regex_constants::match_default ); | (2) | (since C++11)
template< class CharT, class Alloc, class Traits > bool regex_match( const CharT* str, std::match_results<const CharT*, Alloc>& m, const std::basic_regex<CharT, Traits>& e, std::regex_constants::match_flag_type flags = std::regex_constants::match_default ); | (3) | (since C++11)
template< class CharT, class Traits > bool regex_match( const CharT* str, const std::basic_regex<CharT, Traits>& e, std::regex_constants::match_flag_type flags = std::regex_constants::match_default ); | (4) | (since C++11)
template< class STraits, class SAlloc, class Alloc, class CharT, class Traits > bool regex_match ( const std::basic_string<CharT, STraits, SAlloc>& s, std::match_results <typename std::basic_string<CharT, STraits, SAlloc>::const_iterator, Alloc>& m, const std::basic_regex<CharT, Traits>& e, std::regex_constants::match_flag_type flags = std::regex_constants::match_default ); | (5) | (since C++11)
template< class STraits, class SAlloc, class CharT, class Traits > bool regex_match( const std::basic_string<CharT, STraits, SAlloc>& s, const std::basic_regex<CharT, Traits>& e, std::regex_constants::match_flag_type flags = std::regex_constants::match_default ); | (6) | (since C++11)
template< class STraits, class SAlloc, class Alloc, class CharT, class Traits > bool regex_match ( const std::basic_string<CharT, STraits, SAlloc>&&, std::match_results <typename std::basic_string<CharT, STraits, SAlloc>::const_iterator, Alloc>&, const std::basic_regex<CharT, Traits>&, std::regex_constants::match_flag_type flags = std::regex_constants::match_default ) = delete; | (7) | (since C++11)

Determines if the regular expression e matches the entire target character sequence. The detailed match result is stored in m (if present).

1,2) The target character sequence is represented by the range `[`first`,` last`)`.

If `BidirIt` does not satisfy the requirements of LegacyBidirectionalIterator, the behavior is undefined. | (until C++23)
If `BidirIt` does not model `bidirectional_iterator`, the behavior is undefined. | (since C++23)

3,4) The target character sequence is represented by the range `[`str`,` str + std::char_traits<CharT>::length(str)`)`.
5,6) The target character sequence is represented by the string s.
7) The target character sequence cannot be represented by a std::string rvalue.

If the match does not exist, the following expressions involving m (if exists) should yield the specified values:

Expression | Value
--- | ---
m.`ready`() | true
m.`size`() | ​0​
m.`empty`() | true

If the match exists, given any integer in `(`​0`,` m.size()`)` as n, the following expressions involving m should yield the specified values for each overload listed below:

Expression | Value
--- | ---
Overload (1) | Overload (3) | Overload (5)
m.`ready`() | true
m.`size`() | 1 + e.`mark_count`()
m.`empty`() | false
m.`prefix`().first | first | str | s.begin()
m.`prefix`().second
m.`prefix`().matched | false[1]
m.`suffix`().first | last | std::char_traits<CharT>:: length(str) + str | s.end()
m.`suffix`().second
m.`suffix`().matched | false[2]
m`[0]`.first | first | str | s.begin()
m`[0]`.second | last | std::char_traits<CharT>:: length(str) + str | s.end()
m`[0]`.matched | true[3]
m`[n]`.first | last if marked sub-expression n did not participate in the match the start of the sequence otherwise matching sub-expression n otherwise
m`[n]`.second | last if marked sub-expression n did not participate in the match the end of the sequence otherwise matching sub-expression n otherwise
m`[n]`.matched | false if marked sub-expression n did not participate in the match true otherwise

1. ↑ The match prefix is empty.
2. ↑ The match suffix is empty.
3. ↑ The entire sequence is matched.

### Parameters

first, last | - | the target character range
str | - | the target null-terminated C-style string
s | - | the target std::basic_string
m | - | the match results
e | - | the regular expression
flags | - | flags used to determine how the match will be performed

### Return value

Returns true if the entire target sequence matches e, false otherwise.

### Notes

Because `regex_match` only considers full matches, the same regex may give different matches between `regex_match` and std::regex_search:

    std::regex re("Get|GetValue");
    std::cmatch m;
    std::regex_search("GetValue", m, re);  // returns true, and m[0] contains "Get"
    std::regex_match ("GetValue", m, re);  // returns true, and m[0] contains "GetValue"
    std::regex_search("GetValues", m, re); // returns true, and m[0] contains "Get"
    std::regex_match ("GetValues", m, re); // returns false

### Example

Run this code

    #include <cstddef>
    #include <iostream>
    #include <regex>
    #include <string>

    int main()
    {
        // Simple regular expression matching
        const std::string fnames[] = {"foo.txt", "bar.txt", "baz.dat", "zoidberg"};
        const std::regex txt_regex("[a-z]+\\.txt");

        for (const auto& fname : fnames)
            std::cout << fname << ": " << std::regex_match(fname, txt_regex) << '\n';

        // Extraction of a sub-match
        const std::regex base_regex("([a-z]+)\\.txt");
        std::smatch base_match;

        for (const auto& fname : fnames)
            if (std::regex_match(fname, base_match, base_regex))
                // The first sub_match is the whole string; the next
                // sub_match is the first parenthesized expression.
                if (base_match.size() == 2)
                {
                    std::ssub_match base_sub_match = base_match[1];
                    std::string base = base_sub_match.str();
                    std::cout << fname << " has a base of " << base << '\n';
                }

        // Extraction of several sub-matches
        const std::regex pieces_regex("([a-z]+)\\.([a-z]+)");
        std::smatch pieces_match;

        for (const auto& fname : fnames)
            if (std::regex_match(fname, pieces_match, pieces_regex))
            {
                std::cout << fname << '\n';
                for (std::size_t i = 0; i < pieces_match.size(); ++i)
                {
                    std::ssub_match sub_match = pieces_match[i];
                    std::string piece = sub_match.str();
                    std::cout << "  submatch " << i << ": " << piece << '\n';
                }
            }
    }

Output:

    foo.txt: 1
    bar.txt: 1
    baz.dat: 0
    zoidberg: 0
    foo.txt has a base of foo
    bar.txt has a base of bar
    foo.txt
      submatch 0: foo.txt
      submatch 1: foo
      submatch 2: txt
    bar.txt
      submatch 0: bar.txt
      submatch 1: bar
      submatch 2: txt
    baz.dat
      submatch 0: baz.dat
      submatch 1: baz
      submatch 2: dat

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2205 | C++11 | n could be zero in the postcondition | can only be positive
LWG 2273 | C++11 | it was unclear whether partial matches are considered | only considers full matches
LWG 2329 | C++11 | overload (5) accepted `basic_string` rvalues, which could result in dangling iterators | rejected via deleted overload (7)

### See also

basic_regex (C++11) | regular expression object (class template)
match_results (C++11) | identifies one regular expression match, including all sub-expression matches (class template)
regex_search (C++11) | attempts to match a regular expression to any part of a character sequence (function template)

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